Question: plot functions in the same figure

i want to plot these four functions in the same graphe f(x)=1/1+x^2 on the intervalle [0,1] also the second function the line curve that connects the two points(0,f(0)) and (1/3,f(1/3)), the third function the line curve that connects the two points (1/3,f(1/3)) and (2/3,f(2/3)), the fourth function the line curve that connects the two points (2/3,f(2/3)) and (1,f(1))

can anyone help me ?

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